1. Field of the Invention
This invention relates to an apparatus for recording/reproducing and a method for controlling rotation of a recording medium, and more particularly relates to an apparatus for recording/reproducing a method for controlling rotation of a recording medium which are capable of reducing polarity fluctuation of error signals due to noise and performing accurately rotation control.
2. Description of Related Art
Heretofore, as the method for controlling rotation of a disc, two methods, which include a method that a rotation control signal is generated using a synchronizing signal of a signal recorded in a disc as data, and another method that a rotation control signal is generated using a reproducing signal from an address information recorded by wobbling of a track on a disc with a certain period, have been known.
In these rotation control methods, speed term data and phase term data at the irradiated position are generated based on the light reflected from a disc, and these data are synthesized to obtain an error voltage used for rotation control.
Polarity of the error voltage for indicating the rotation direction (acceleration or deceleration) of a disc and magnitude of the error voltage (absolute value) are obtained, and the signals of polarity and absolute value are synthesized and supplied to a certain spindle motor.
FIG. 9 shows an exemplary structure of a conventional polarity judgment circuit for judging polarity of an error voltage. In detail, an error voltage and a predetermined reference voltage are supplied to a comparator 1, and these two voltages are compared. A signal which indicates positive polarity (acceleration) is outputted if the error voltage is higher than the reference voltage, and a signal which indicates negative polarity (deceleration) is outputted if the error voltage is lower than the reference voltage.
FIG. 10 shows an error voltage for rotation control generated from a record signal on a disc. An error voltage is composed of a rotation variation voltage component which varies periodically every rotation, a certain constant loss voltage, and noise voltage having small amplitude.
On the other hand, FIG. 11 shows an error voltage generated from a wobble signal. Also in this case, though the error voltage is composed of rotation variation voltage, loss voltage, and noise components, fluctuation due to noise is more significant in comparison with the error voltage generated from a record signal shown in FIG. 10.
As it is apparent from FIG. 10 and FIG. 11, an error voltage includes always positive polarity (polarity of the direction which accelerates rotation). In detail, assuming that the reference voltage in FIG. 9 is 0, then the output from the comparator 1 shows always positive polarity corresponding to the error voltage input shown in FIG. 10 and FIG. 11.
In order to perform higher speed recording/reproducing processing of data, it is considered that rotation speed of a disc is increased to increase transfer speed of data.
FIG. 12A shows an error voltage generated from a record signal on a disc in the case that rotation speed is increased more faster than the case shown in FIG. 10. FIG. 12B shows polarity of the error voltage in such case. As shown in FIG. 12B, the increased rotation speed results in negative polarity, namely, generation of a voltage for deceleration.
FIG. 13A shows an error voltage generated from a wobble signal in the case of increased rotation speed. FIG. 13B shows polarity of the error voltage in such case. Inversion between positive polarity and negative polarity occurs more often in the case of FIG. 13B than in the case of FIG. 12B. The often inversion is attributed to error voltage fluctuation due to noise more significant in the case of FIG. 13 than in the case of FIG. 12.
Therefore, in the case that transfer speed is intended to be increased by rotating a disc faster, often inversion of polarity which arises along with judgment of polarity of the error voltage generated from a wobble signal results in loud deceleration noise and increased power consumption when decelerating, such noise and power consumption are problems.